May Day marches and rallies drew thousands of participants and created hectic traffic Tuesday as protesters attempt to call attention to what they say are necessary changes to immigration policies, workers rights and other social issues.

The march down Broadway was peaceful. However, a splinter group on Hill and 4th streets became involved in a skirmish with police after an object was thrown in the direction of officers. The officers apparently had blocked some protesters from vandalizing property.

A female officer was struck with a skateboard around 4 p.m. at the intersection. Two suspects were detained for assault with a deadly weapon on a police officer, but they were not arrested. The officer was taken to the hospital. Police were searching for the assailant.

Violence was more widespread in Seattle and Oakland.

In Seattle, black-clad protesters used sticks to smash small downtown windows and ran through the streets disrupting traffic. At least two people were arrested. Police have made at least two arrests.

In Oakland, police fired tear gas and "flash-bang" grenades to disperse the crowds in a downtown intersection where they were demonstrating.

Other protests were held in various parts of the U.S., including New York, Chicago and Atlanta.

Anyone living or working in downtown L.A. braced for many street closures throughout the day. Anyone who planned to visit downtown Tuesday was advised to plan ahead or avoid the area completely.

Broadway from Olympic Boulevard to Temple Street was most heavily affected. Demonstrators converged to that area around 1 p.m. for one massive march, though there were waves of marches that followed. Cross streets along Broadway from 11th Street to Temple Street were also affected. Other evening time rallies will follow, including one at Pershing Square at 7 p.m.

As many as 48 bus lines were expected to be delayed or detoured throughout the day as a result of the nearly 25,000 people expected to participate in the marches.

The LAPD planned to minimize the traffic impact by doing rolling closures, depending on the size of the crowd. LAPD Cmdr. Andrew Smith warned commuters getting out of downtown to head south toward the 10 Freeway.

Those attending Tuesday's L.A. Lakers playoff game were warned to arrive as early as possible and even carpool to ease parking and traffic congestion.

LAX worker strike and closures

An estimated 1,200 workers with the United Service Workers West Union at Los Angeles International Airport began their May Day protest at 3 a.m. A march followed at noon and was expected to last until 4 p.m. Century Boulevard between Airport Boulevard was set for closure during that time.

Because airliners are hiring contractors more often, union workers say the move has cut regular staff, disbanded unions and cut healthcare. As a result, they say airlines are making it increasingly difficult to support their families and unionize.

Hundreds of protesters went inside the Tom Bradley International Terminal after noon. They represented workers at LAX who were protesting unsafe working conditions and what they said are management attempts to block their union organizing.

Inside the terminal, they were met by politicians like Congresswoman Janice Hahn and Los Angeles Councilman Bill Rosendahl.

The protestors left the Bradley terminal in a pre-planned, pre-arranged march through other terminals on the airport's north side. Police escorts cleared the way.

There was little or no disruption of people trying to board planes, only minor inconveniences. Eighteen people had agreed to be arrested later at Avion Drive and Century Boulevard.

Despite the expected closures, airport police continued to work to make sure no flights were delayed. Still, anyone headed to LAX was advised to take Sepulveda Boulevard or the 105 Freeway during the march, and to allow an extra hour to catch a flight.

Occupy L.A.'s role in May Day 2012

Occupy L.A. wasn't absent from May Day protests. They staged four marches from all corners of L.A. One group met at Panorama High School on Van Nuys Boulevard in Panorama City, another group gathered at Wilshire Boulevard and Ocean Avenue in Santa Monica, a third group met at California State University, Dominguez Hills and the final group met at Avenida Cesar Chavez and Atlantic Boulevard near East L.A. College.

Occupy protesters set up a website for the May Day march, detailing their plan to disrupt business, particularly in Downtown L.A.'s financial district. They also wanted to bring attention to social injustices like police brutality.

About 100 people gathered in East L.A. near a Carl's Jr. where a man was fatally shot by police earlier this year after he used a lead pipe to smash in the restaurant's windows. They say meeting there was part of a significant example of the police brutality they want to see end.

Protester Jamie Garcia highlighted other issues of importance to the group, like access to education and healthcare.

"Right now I think the community needs to come together and start asking the right questions," she said. "Asking where all the money for the bailouts went, asking if we did bailout these big banks, why are we still in this current situation." She added the money would be better spent in the community through healthcare and education instead of going to police officers and war.

The group also drew attention to economic inequality by stopping to feed the homeless along Skid Row during their march.

Occupy protesters in Van Nuys carried banners and drums to the Van Nuys Civic Center in support of legalizing illegal immigrants and stopping deportation before heading downtown. Parts of Van Nuys Boulevard were closed as police escorted the crowd, which was made up of various local community groups and students who skipped school to participate.

Protesters, police hope for peaceful May Day

Last year's May Day marches were peaceful. Dozens of peace officers will be on-hand again this year because they say they want to protect protesters' First Amendment rights.

But the May Day march hasn't always been peaceful. Five years ago, the May Day protest at MacArthur Park was named the May Day melee after LAPD officers used rubber bullets, bean bag rounds and batons to disperse the crowd. Forty-two people were injured, including six members of the media. Those injured sued the city and won. The LAPD has undergone a lot of training in the years following the May Day melee. L.A. City firefighters and paramedics were scheduled to be on-hand.

The LAPD did issue special event permits for the May Day marches and rallies and will monitor events to ensure they are peaceful.